Hydrofluorocarbons (HFCs) and in particular hydrofluoroolefins (HFOs), such as 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf), are compounds known for their properties of refrigerants and heat-exchange fluids, extinguishers, propellants, foaming agents, blowing agents, gaseous dielectrics, polymerization medium or monomer, support fluids, agents for abrasives, drying agents and fluids for energy production units.
HFOs have been identified as desirable alternatives to HCFC as a result of their low ODP (ozone depletion potential) and GWP (global warming potential) values.
Most of the processes for the manufacture of hydrofluoroolefins involve a fluorination and/or dehydrohalogenation reaction. This type of reaction is carried out in the gas phase and generates impurities which consequently have to be removed in order to obtain the desired compound in a sufficient degree of purity for the applications targeted.
For example, in the context of the production of 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf), the presence of impurities, such as 1-chloro-3,3,3-trifluoro-1-propene (HCFO-1233zd), 1,3,3,3-tetrafluoro-1-propene (HFO-1234ze) and 1,1,1,3,3-pentafluoropropane (HFC-245fa), is observed. These impurities are isomers of the main compounds targeted at being obtained by the process for the production of 2,3,3,3-tetrafluoro-1-propene, besides the latter, i.e. 2-chloro-3,3,3-trifluoro-1-propene (HCFO-1233xf) and 1,1,1,2,2-pentafluoropropane (HFC-245cb). In view of the respective boiling points of 1-chloro-3,3,3-trifluoro-1-propene (HCFO-1233zd), 1,3,3,3-tetrafluoro-1-propene (HFO-1234ze) and 1,1,1,3,3-pentafluoropropane (HFC-245fa), these can accumulate in the reaction loop and thus prevent the formation of the products of interest.
The purification of this type of reaction mixture can be carried out by various techniques known from the prior art, such as, for example, distillation. However, when the compounds to be purified have boiling points which are too close or when these form azeotropic or quasi-azeotropic compositions, distillation is not an effective process. Extractive distillation processes have thus been described.
EP 0 864 554 discloses a process for the purification of a mixture comprising 1,1,1,3,3-pentafluoropropane (HFC-245fa) and trans-1-chloro-3,3,3-trifluoro-1-propene (HCFO-1233zd) by distillation in the presence of a solvent having a boiling point which is greater than that of trans-1-chloro-3,3,3-trifluoro-1-propene.
WO 03/068716 discloses a process for the recovery of pentafluoroethane from a mixture comprising pentafluoroethane and chloropentafluoroethane by distillation in the presence of hexafluoropropene.
Also, WO 98/19982 discloses a process for the purification of 1,1-difluoroethane by extractive distillation. The process consists in bringing an extraction agent into contact with a mixture of 1,1-difluoroethane and vinyl chloride. The extraction agent is chosen from hydrocarbons, alcohols and chlorocarbons having a boiling point of between 10° C. and 120° C. As mentioned by WO 98/19982, the selection of the extraction agent can prove to be complex depending on the products to be separated. WO 2013/088195 discloses a process for the preparation of 2,3,3,3-tetrafluoropropene from 1,1,1,2,3-pentachloropropane and/or 1,1,2,2,3-pentachloropropane. There thus still exists a need for the implementation of a specific process for the purification of 2,3,3,3-tetrafluoro-1-propene.